The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
It is known to use a catalytic converter in the exhaust gas flow path of a motor vehicle with an internal combustion engine. The catalytic converter includes a substrate with a coating of a catalyst material that catalyzes the oxidation of hydrocarbon molecules and carbon monoxide molecules as well as the reduction of nitrogen oxides emitted in the vehicle exhaust gas. The catalyst performs efficiently when the catalyst is above a minimum temperature to stimulate the desired catalytic reactions and the exhaust gas has the proper fuel to air (F/A) ratio.
It is desirable to optimize the fuel to air ratio delivered to the engine for performance as well as emissions control. Emissions control is increasingly difficult at startup because a higher fraction of delivered fuel remains unburned and is subsequently exhausted, and the catalyst has not reached its operating temperature. Methods have been employed to reduce exhaust emissions and increase catalytic converter performance including increasing engine speed at idle, retarding ignition timing and/or reducing delivered fuel.
One method for improving catalytic converter performance during startup is by utilizing a secondary air injection reaction (SAIR) system. The output of a secondary air injection (SAI) pump can be disposed in the exhaust system upstream of the catalytic converter and be used to inject air into the exhaust to react with unburned and partially burned fuel from the engine in order to heat up the catalyst.
During operation of the engine, it may be useful to detect an SAI failure (such as a leak and/or blockage) in the pipe upstream of an SAI valve associated with the SAIR system. It may also be useful to detect such a fault downstream of the SAI valve of the SAIR system. While some control systems have been able to adequately detect such failures upstream of the SAI valve, it can be difficult to detect failures downstream of the SAI valve.